As CEO Tim Cook pointed out, with each new product category Apple created a new UI: the Mac's mouse, the iPod's clickwheel, the iPhone's multi-touch. For the Apple Watch, there is the Digital Crown.

The Digital Crown, a souped-up dial on the right side, provides a way to scroll, zoom and navigate the Apple Watch without covering the display. A wearer can scroll through lists and messages, make selections and more without obstructing the screen.

From CEO Tim Cook: "What we DIDN'T do is shrink down the iPhone interface and put it on your wrist. That'd be a horrible experience!"

Interactivity and Communication

The watch will have Siri, Maps and Photos apps, among others. The Maps app shows the way and guides wearers to go left or right with a tap. From a feature called Friends, wearers can make a call, send a message, customize emojis or a sketch made with their finger.

They're putting Siri on the new Apple Watch so finally you can feel like a secret agent talking into your sleeve. #AppleLive

There's also a feature called "Glances," which you swipe up from the bottom of the screen to see stocks, meetings, weather and world time.

Wearers can also send their friends a "gentle tap on the wrist" through haptic feedback (or tiny vibrations), even if they are thousands of miles away. They can also capture and send their heartbeat by pressing two fingers on the screen.

More than a Health Tracking Device

Apple is pushing the watch heavily toward fitness-savy consumers. A "Workout" app will monitor calories burned and miles run, and an "Activity" app will show the same metrics over the course of a day.

The watch measures three aspects of movement inside "rings": Move, Exercise and Stand. The Move ring gives an overview of how active the wearer is, while the Exercise ring measures brisk activity, and the Stand ring shows how often the wearer has stood up to take a break from sitting.

There are three watch collections: the Apple Watch, made with stainless steel; the Apple Watch Sport, inside an aluminum casing; and the Apple Watch Edition, made of 18k gold. There is also a smaller-sized watch for smaller wrists.

For the bands, there are six different versions, made of leather, polymer, metal mesh and stainless steel, and each has a mechanism that makes the straps interchangeable.

The screen is made of ultra-durable sapphire, resistant to cracks. Wearers can personalize the capabilities and appearance of the faces.